Water-based ballpoint pen

ABSTRACT

A water-based ballpoint pen including a specific aqueous ink, a ball, a ballpoint pen tip that holds the ball at a front end of the ballpoint pen tip, an ink follower following the ink with consumption of the ink, and an ink container directly containing the ink and the ink follower. The ink container communicates with a rear portion of the tip. The ink follower includes at least a base oil and a thickener. The ball point pen tip discharges the ink from the top end portion. The ink container supplies the ink to the tip.

This is a continuation of application Ser. No. 10/840,620 filed May 7,2004. The entire disclosures of the prior application, application Ser.No. 10/840,620 is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a water-based ballpoint pen. Thewater-based ballpoint pen comprises an aqueous ink and an ink followerdirectly filled in the ink container thereof, and is so designed thatthe ink follower follows the ink with the consumption of ink therein andprevents the ink from leaking out from the back end of the inkcontainer.

BACKGROUND ART

Heretofore, an oil-based ballpoint pen is disclosed, which comprises anoily ink directly filled in the ink container thereof that has aballpoint pen tip fitted into one end thereof and in which the tip holdsa ball at its top end.

The number of the constitutive members thereof is small and theoil-based ballpoint pen of the type is inexpensive. Because of itsconstitution as above, however, the oil-based ballpoint pen has someproblems. Concretely, when the pen is left with its tip downward, thenink may drop out from the gap between the ball and the tip end. In orderto prevent such ink dropping, the gap between the two is extremelynarrowed and the ink is made to have an extremely high viscosity of fromabout 10 to 20 Pa·s or so at room temperature. Accordingly, the penoften feels heavy while writing with it, and tends to give thin lettersor images.

On the other hand, a water-based ballpoint pen that is filled with alow-viscosity aqueous ink feels light while writing with it, and maygive thick letters or images, but it requires a mechanism for ink flowcontrol and is therefore defective in that its structure is complicatedand it is expensive.

Further, a shear-thinning ballpoint pen has been disclosed recently,which comprises an oil-based ballpoint pen mechanism structure mentionedabove and contains a shear-thinning aqueous ink and an ink followerfilled therein (for example, see Patent Reference 1).

Like the above-mentioned oil-based ballpoint pen, the shear-thinningballpoint pen is inexpensive and its structure is simple, and, inaddition, the ink contained in it has a high viscosity while keptstatically with no shearing stress applied thereto, and it is stablyheld in the ballpoint pen mechanism. On the other hand, while in writingwith the pen, the viscosity of the ink alone around the ball is loweredowing to the high shear force of the ball that rotates at high speed,and, as a result, the ink may smoothly run through the gap between theball and the ball-holding area around it owing to the capillary forcethereof, and is therefore transferred onto the surface of paper.

Accordingly, when writing with it, the pen may give thick letters andimages and may feel lighter than oil-based ballpoint pens. Theshear-thinning ink for the pen is controlled to have a shear-thinningindex of from 0.1 to 0.6 or so in order that it is prevented fromleaking out from the tip end of the pen while in writing with it, andthe viscosity of the ink in writing under shear force applied thereto isnot so high as compared with that of oily ink. However, when comparedwith water-based ballpoint pens, the feel in writing with theshear-thinning ballpoint pen is not so good, and, in addition, at thestart of writing with it, the ink is often difficult to transfer to theball.

Moreover, the letters and images written with the shear-thinning ink aredifficult to dry, and when they are felt with fingers or rubbed witheach other, they may be often transferred onto the non-writtenbackground area to stain it.

[Patent Reference 1]

U.S. Pat. No. 4,545,818

SUMMARY OF THE INVENTION

The invention is to solve the above-mentioned problems with conventionalballpoint pens, and is to provide a ballpoint pen which has a relativelysimple structure and is inexpensive and which has good writingproperties in that it feels light while writing with it and gives thickletters and images and that it can write well from the start of writingwith it and the letters and images written with it may dry rapidly.

Specifically, the invention has a following constitution.

(1) A water-based ballpoint pen comprising:

an aqueous ink;

a ball;

a ballpoint pen tip for holding said ball at a front end thereof and fordischarging said ink from said top end portion;

an ink follower following said ink with consumption of said ink; and

an ink container directly containing said ink and said ink follower andfor supplying said ink to said tip, said ink container communicatingwith a rear portion of said tip,

wherein the ink is selected from (i) a shear-thinning aqueous ink thathas a viscosity of from 3 to 160 mPa·s, measured with an E-type rotaryviscometer at 20° C. and at 100 rpm, and has a shear-thinning index offrom 0.9 to 0.99, and (ii) a non-shear-thinning aqueous ink having aviscosity of from 1 to 50 mPa·s, measured with an B-type rotaryviscometer at 20° C., and

wherein the ink follower comprises at least a base oil and a thickenerand satisfies that the point (ω) at which its tan δ in viscoelasticitydetermination exceeds 1 falls within a range of 20 rad/s≦ω≦450 rad/s.

(2) The water-based ballpoint pen according to the above (1), whereinthe base oil of the ink follower is at least one selected frompolybutene and silicone oil and the thickener thereof is at least oneselected from fatty acid amide or silica.

(3) The water-based ballpoint pen according to the above (1) or (2),further comprising an elastic member that urges the ball toward thefront end of the tip when no stress is applied to the ball, and whereinthe ball is retractable from the front end of the tip when stress isapplied to the ball.

(4) The water-based ballpoint pen according to any one of the above (1)to (3), which further comprises a solid ink follower combined with theink follower.

(5) The water-based ballpoint pen according to any one of the above (1)to (4), which further comprises:

a ball point pen refill containing the ink container, the ink containercommunicating with a rear portion of said tip;

a tubular member containing said ball point pen refill, wherein the tipis retractably projected from a front end of the tubular member.

(6) The water-based ballpoint pen according to the above (5), furthercomprising a spring disposed in the tubular member to urge the ballpoint pen refill toward a rear portion of the tubular member, whereinthe tip is projected from the front end of the tubular member when theball point refill is pressed toward the front end of the tubular memberagainst an urging force of the spring.

(7) The water-based ballpoint pen according to the above (5) or (6),further comprising a clip formed on the front outside of the tubularmember.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section of the embodiment of a water-basedballpoint pen refill used in the invention.

FIG. 2 is an explanatory drawing of the section of a water-basedballpoint pen of haunting type wherein the water-based ballpoint penrefill shown in FIG. 1 is inserted into the tubular member as acartridge.

FIG. 3 is an another explanatory drawing of the longitudinal section ofa water-based ballpoint pen of haunting type wherein the water-basedballpoint pen refill shown in FIG. 1 is inserted into the tubular memberas a cartridge.

In Figs., sign 1 is a water-based ballpoint pen refill, sign 2 is aballpoint pen tip, sign 3 is a ball, sign 4 is a elastic member, sign 41is a rod, sign 42 is a coil, sign 43 is a tube swelling, sign 5 is aconnecting member, sign 51 is a hooking projection, sign 6 is an inkcontainer, sign 61 is an ink, sign 62 is an ink follower, sign 7 is atail stopper, sign 71 is a vent hole, sign 8 is a water-based ballpointpen of haunting type, sign 81 is a tubular member, sign 82 is a spring,sign 83 is a clip.

DETAILED DESCRIPTION OF THE INVENTION

The ballpoint pen tip may have any conventional and popular tipstructure heretofore known in the art. For example, a metal is machinedinto a tube having a ball receiver and an ink guide formed inside it; ora metal pipe is worked to form a plurality of inner projections on theinner face at around the top end thereof by pressure deformation fromthe outer surface thereof, and ink flow grooves that radially extendfrom the center part toward the outside in the radical direction thereofare formed between the inner projections. In particular, the tip formedby the pressure deformation enables a good writing feel at a low writingpressure, since the contact area thereof with the back end of the ballin the tip is relatively small.

The ball to be held in the ballpoint pen tip is effectively a ballformed of hard metal, stainless steel, ruby, ceramics or the like andhaving an outer diameter of from 0.3 to 1.5 mm; and the movable distanceof the ball in the radial direction thereof between the inner diameterof the ball-holding part of the tip and the ball is preferably from 10to 50 μm, and the movable distance of the ball in the axial direction ispreferably from 10 to 30 μm.

Preferably, the ballpoint pen tip has an elastic member that springs theback end of the ball in the forward direction thereof, in which theelastic member is so designed that it presses the ball against the inneredge of the front (top) end of the tip to form a closed condition duringnon-writing, but, during writing, the ball is moved backward owing tothe writing pressure thereto to discharge the ink from the front top endportion of the tip. Having the constitution, the ballpoint pen preventsink leakage from it while it is not in use.

Examples of the elastic member are a spring of fine metal wire, arod-combined metal spring constructed by bonding a straight part (rod)to one end of the metal spring, and a plastic spring formed by working alinear plastic. Having a spring force of from 15 to 45 g, the elasticmember is constituted to be pressable and applied to the pen tip.

The ink container that is bonded to the ballpoint pen tip directly orvia a connecting member may be any popular tubular member, for which,for example, usable are shaped members of thermoplastic resin such aspolyethylene, polypropylene or polyethylene terephthalate. These arefavorable as they well retard vaporization of ink and their productivityis good.

The ink container preferably has an inner diameter of from 2.5 to 10 mm.

Also preferably, the ink container is formed of a transparent, coloredtransparent or semitransparent shaped article, as it enables to confirmthe ink color and the ink quantity through it.

The ink container may form a refill to be inserted into a tubularmember, or may have a tip fitted to the top thereof to form a tubularmember and the tubular member may be directly filled with ink.

The ballpoint pen of a type wherein the refill is contained in thetubular member can be of a knock type such as back-end knock type orside knock type wherein the above-described refill is prepared so as togo in and out without using a cap or of a rotary type in addition to aballpoint pen wherein a cap is used.

The ink to be directly filled in the ink container may be any oneselected from a shear-thinning aqueous ink that has a viscosity (20° C.)of from 3 to 160 mPa·s, measured with an EM-type rotary viscometer at100 rpm, and has a shear-thinning index of from 0.9 to 0.99, or anon-shear-thinning aqueous ink having a viscosity at 20° C. of from 1 to50 mPa·s. The shear-thinning index is a value, n, in the experimentalformula T=Kj^(n) (where K and n are calculated constants) that isderived through viscometric rheological determination of the shearstress value (T) and the shear rate (j) of the ink.

Conventional materials known for providing shear-thinning properties canbe used in the shear-thinning aqueous ink. Examples of such materialsare water-soluble or dispersible, xanthan gum, welan gum, succinoglycan(organic acid-modified heteroglycan composed of glucose unit andgalactose unit, having a mean molecular weight of from about 100 to8,000,000), guar gum, locust bean gum and its derivatives, hydroxyethylcellulose, alkyl alginates, polymers mainly comprising alkylmethacrylate and having a molecular weight of from 100,000 to 150,000,glycomannan, thickening polysaccharides having a gelling property andextracted from seaweed such as agar and carrageenan, benzylidenesorbitoland benzylidenexylitol and their derivatives, crosslinking acrylic acidpolymers, inorganic fine particles, nonionic surfactants having HLB offrom 8 to 12 such as polyglycerin fatty acid esters,polyoxyethylenesorbitan fatty acid esters, polyethylene glycol fattyacid esters, polyoxyethylene castor oil, polyoxyethylene lanolin-lanolinalcohol-bees wax derivatives, polyoxyethylene alkylether-polyoxypropylene alkyl ethers, polyoxyethylene alkylphenyl ethers,fatty acid amides, as well as salts of dialkyl ordialkenylsulfosuccinates. These can be used either singly or ascombined.

In addition, a mixture of N-alkyl-2-pyrrolidone and anionic surfactant,and a mixture of polyvinyl alcohol and acrylic resin can also be used.

The amount of the shear-thinning agent to be added to the ink may besuitably varied within a range within which the ink may have theshear-thinning index defined herein.

The shear-thinning property of the ink indicates the rheologicalproperty thereof, and it means that the ink is highly viscous and ishardly fluid when it is in a static condition or when it receives a lowstress, but its viscosity lowers and it becomes well fluid when itreceives an increased stress. Therefore, the shear-thinning property mayalso be referred to as a thixotropic or pseudoplastic liquid property.Accordingly, while used for writing with it under a high shear stressapplied thereto, the three-dimensional structure of the ink compositionis temporarily broken and the viscosity thereof is therefore lowered. Asa result, the viscosity of the ink at the top end of a ballpoint penlowers suitably for writing with it, and the ink is thereforetransferred onto the surface of paper. While not used for writing, theink has a high viscosity and is prevented from leaking out of aballpoint pen, and, in addition, separation and back flow of the ink mayalso be prevented. Further, the physical properties of the ink can bekept stable for long.

For the colorant to be in the ink, usable are all dyes and pigmentssoluble or dispersible in aqueous media, and their examples arementioned below.

Acid dyes, basic dyes and direct dyes are usable in the ink.

The acid dyes include:

-   New Coccine (C.I. 16255),-   Tartrazine (C.I. 19140),-   Acid Blue Black 10B (C.I. 20470),-   Guinea Green (C.I. 42085),-   Brilliant Blue FCF (C.I. 42090),-   Acid Violet 6B (C.I. 42640),-   Soluble Blue (C.I. 42755),-   Naphthalene Green (C.I. 44025),-   Eosine (C.I. 45380),-   Phloxine (C.I. 45410),-   Erythrosin (C.I. 45430),-   Nigrosine (C.I. 50420),-   Acid Flavin (C.I. 56205).

The basic dyes include:

-   Chrysoidine (C.I. 11270),-   Methyl Violet FN(C.I. 42535),-   Crystal Violet (C.I. 42555),-   Malachite Green (C.I. 42000),-   Victoria Blue FB (C.I. 44045),-   Rhodamine B (C.I. 45170),-   Acridine Orange NS (C.I. 46005),-   Methylene Blue B (C.I. 52015).

The direct dyes include:

-   Congo Red (C.I. 22120),-   Direct Sky Blue 5B (C.I. 24400),-   Violet BB (C.I. 27905),-   Direct Deep Black EX (C.I. 30235),-   Kayarus Black G Conc (C.I. 35225),-   Direct Fast Black G (C.I. 35255),-   Phthalocyanine Blue (C.I. 74180).

The pigments include inorganic pigments such as carbon black andultramarine; organic pigments such as copper phthalocyanine blue andbenzidine yellow; and aqueous pigment dispersions prepared by finely andstably dispersing pigment in aqueous media by the use of surfactant orresin. Their examples are as follows:

-   C.I. Pigment Blue 15:3B (trade name, Sandye Super Blue GLL by Sanyo    Dye, having a pigment content of 24%),-   C.I. Pigment Red 146 (trade name, Sandye Super Pink FBL by Sanyo    Dye, having a pigment content of 21.5%),-   C.I. Pigment Yellow 81 (trade name, TC Yellow FG by Dainichi Seika    Kogyo, having a pigment content of about 30%),-   C.I. Pigment Red 220/166 (trade name, TC Red FG by Dainichi Seika    Kogyo, having a pigment content of about 35%).

The resin for dispersing the pigment includes polyamide resin,polyurethane resin, polyester resin, epoxy resin, melamine resin,phenolic resin, silicone resin, polyvinyl alcohol, polyvinylpyrrolidone,polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride,polystyrene, acrylic acid resin, maleic acid resin, gum arabic,cellulose, dextran, casein, and their derivatives, as well as copolymersof the above-mentioned resins.

Particulate fluorescent pigments in synthetic resin are also usableherein, which are produced by dispersing a solid solution of fluorescentdye in resin matrix.

In addition, further usable herein are white pigments such as titaniumdioxide; metal powders such as aluminium powder; pearl pigments preparedby coating the surface of a core substance selected from natural mica,synthetic mica, alumina or glass powder with a metal oxide such astitanium dioxide; and cholesteric liquid-crystal brilliant pigments.

For the solvent to be in the ink, usable are water and conventionalwater-soluble organic solvents that are generally used in the art. Theirexamples are ethanol, propanol, butanol, glycerin, sorbitol,triethanolamine, diethanolamine, monoethanolamine, ethylene glycol,diethylene glycol, thiodiethylene glycol, hexylene glycol,1,3-butanediol, neoprene glycol, polyethylene glycol, propylene glycol,butylene glycol, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, ethylene glycol monomethyl ether acetate, propyleneglycol monomethyl ether, propylene glycol monoethyl ether,2-pyrrolidone, N-methyl-2-pyrrolidone.

One or more such water-soluble organic solvents may be used eithersingly or as combined. The amount of the solvent to be in the ink may befrom 2 to 60% by weight, preferably from 5 to 35% by weight.

If desired, the ink may contain a pH-controlling agent, and apreservative or a mildew-proofing agent.

The pH-controlling agent includes ammonia, sodium carbonate, sodiumphosphate, sodium hydroxide, sodium acetate and other inorganic salts,as well as organic basic compounds, for example, water-soluble aminecompounds such as triethanolamine and diethanolamine.

The preservative or mildew-proofing agent includes carbolic acid,1,2-benzisothiazolin-3-one sodium salt, sodium benzoate, sodiumdehydroacetate, potassium sorbate, propyl paraoxybenzoate,2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine.

In addition, a fluorine-containing surfactant as well as a nonionic,anionic or cationic surfactant for improving solvent penetrability, anda defoaming agent such as dimethylpolysiloxane may also be added to theink.

One or more water-soluble resins such as alkyd resin, acrylic resin,styrene-maleic acid copolymer, cellulose derivative,polyvinylpyrrolidone, polyvinyl alcohol and dextrin may also be added tothe resin within a range thereof not interfering with the dryingresistance of the ink; and one or more wetting agents such as urea,nonionic surfactant, sorbitol, mannitol, sucrose, glucose, reducingstarch hydrolyzate and sodium pyrophosphate may also be added thereto.

Further, a rustproofing agent and a lubricant may also be added to theink.

The rustproofing agent includes benzotriazole and its derivatives,tolyltriazole, dicyclohexylammonium nitrite, diisopropylammoniumnitrite, sodium thiosulfate, salts of ethylenediaminetetraacetic acid,saponin, dialkylthiourea.

The lubricant includes metal soap, polyalkylene glycol fatty acidesters, ethylene oxide-added cationic activator, phosphate-typeactivator, salts of thiocarbamic acid, salts of dimethyldithiocarbamicacid.

Preferred examples of the lubricant are compounds of the followinggeneral formula (I) and phosphate-type surfactants described in JP-B1-13508.

wherein R₁ represents an alkyl, alkenyl, phenyl or alkylphenyl grouphaving from 8 to 18 carbon atoms; R₂ represents OH, OM,R—O—(CH₂CH₂O)_(n); M represents an alkali metal, an amine or analkanolamine; n indicates from 1 to 30.

The ink follower is filled into the ink container that contains the ink,at the end edge of the ink therein.

The ink follower comprises a base oil of a known nonvolatile liquid orhardly-volatile liquid such as polybutene, α-olefin oligomer, siliconeoil or pure mineral oil, and a thickener such as silica, aluminiumsilicate, swellable mica or fatty acid amide added to the base oil.

For the base oil of the ink follower, preferred is polybutene orsilicone oil; and for the thickener thereof, preferred is fatty acidamide or silica.

The ink follower for use in the invention is so constituted that thepoint (ω) at which its tan δ in viscoelasticity determination exceeds 1falls within a range of 20 rad/s≦ω≦450 rad/s. The point (ω) ispreferably within a range of 50 rad/s≦ω≦400 rad/s.

This is described in detail. The ink to be in the ballpoint pen is ashear-thinning aqueous ink that has a viscosity of from 3 to 160 mPa·s,measured with an E-type rotary viscometer at 20° C. at 100 rpm, and hasa shear-thinning index of from 0.9 to 0.99, or a non-shear-thinningaqueous ink having a viscosity of from 1 to 50 mPa·s. The staticviscosity of the ink is low, and therefore, the impact resistancethereof is lower than that of conventional shear-thinning ink of whichthe shear-thinning index is controlled to fall between 0.1 and 0.6 orso. Accordingly, the ink may leak out from the end of the ink containerand the ballpoint pen would be useless for writing, and, as a result,the pen would lose its commercial value. In addition, the shear-thinningaqueous ink preferably has a viscosity of from 3 to 100 mPa·s.

In the invention, the ink follower that is to be disposed at the end ofthe ink in the ballpoint pen is made resistant to impact to therebysolve the above-mentioned problems.

The ink follower is viscoelastic, and its property is medium betweenelasticity response and viscosity response.

The viscoelasticity of the ink follower is determined through rheometricoscillation, and the tan δ thereof is a value obtained by dividing theloss modulus by the storage modulus thereof. The ink follower having alower value of tan δ (tan δ<1) is highly elastic and is poorly viscous.On the other hand, the ink follower having a higher value of tan δ (tanδ>1) is poorly elastic and is highly viscous.

In the invention, the region where the angular frequency (rad/d) is 20or more in the above-mentioned viscoelasticity determination is near tothe condition where impact has been given to ballpoint pens, forexample, ballpoint pens have been dropped.

Accordingly, the ink follower of which the viscoelasticity indicated bytan δ is more than 1 at 20 rad/s may have a satisfactory impactresistance depending on the intensity of the viscosity response thereof.

The point at which the above-mentioned value tan δ exceeds 1 is 20 rad/sor more, but if it is more than 450 rad/s, then the elasticity responseof the ink follower may be too strong and the ink follower may lose itsfunction to follow ink, and if so, the ink release from the ballpointpen will be poor.

Accordingly, the ink follower is specifically so constituted that thepoint (ω) at which its tan δ exceeds 1 falls within a range of 20rad/s≦ω≦450 rad/s, whereby it satisfies both good impact resistance andgood writing capability.

The ink follower in the invention may be combined with a solid stopperformed of resin.

EXAMPLES

Examples of the invention are described below, to which, however, theinvention should not be limited. In the following Examples, all partsmean parts by weight.

Preparation of Shear-Thinning Aqueous Ink:

Black Dye [Orient Chemical Industry's C.I. 35255; 40.0 parts trade name,Water Black 100-L having an effective content of 20%] Phosphate-typeSurfactant (lubricant) [Daiichi 1.0 part Kogyo Seiyaku's trade namePlysurf AL] Carbolic Acid (antiseptic) 0.4 parts Triethanolamine(pH-controlling agent) 1.0 part λ-carrageenan (thickener) 0.2 partsDiethylene Glycol 15.0 parts Water 42.4 parts

The colorant and various additives were added to a part of the solventmentioned above. Apart from this, the thickener was added to the otherpart of the solvent. These were mixed and stirred for 1 hour to preparea shear-thinning aqueous ink A.

The viscosity of the ink, measured with an EMD-type rotary viscometer(Toki Sangyo's RE-80R with a standard rotor) at 20° C., was 9.0 mPa·s at100 rpm, and the shear-thinning index thereof was 0.97.

Preparation of Non-Shear-Thinning Aqueous Ink:

Blue Dye [Sumitomo Chemical's C.I. 42655; 7.0 parts trade name, AcidBlue PG] Phosphate-type Surfactant (lubricant) [Daiichi 1.0 part KogyoSeiyaku's trade name Plysurf AL] Carbolic Acid (antiseptic) 0.4 partsTriethanolamine (pH-controlling agent) 1.0 part Polyvinylpyrrolidone(thickener) [BASF's 4.0 parts trade name, Luviskol K-30 having amolecular weight of 40,000] Diethylene Glycol 20.0 parts Water 66.6parts

The colorant and various additives were added to a part of the solventmentioned above. Apart from this, the thickener was added to the otherpart of the solvent. These were mixed and stirred for 1 hour to preparea non-shear-thinning aqueous ink B.

The viscosity of the ink, measured with a B-type rotary viscometer(Tokyo Keiki's BL with a BL adaptor) at 20° C., was 9.5 mPa·s at 60 rpm.

Preparation of Shear-Thinning Aqueous Ink:

Red Dye [Eisen's C.I. 45410, Acid Red 92] 5.0 parts Phosphate-typeSurfactant (lubricant) [Daiichi 1.0 part Kogyo Seiyaku's trade namePlysurf AL] Carbolic Acid (antiseptic) 0.4 parts Triethanolamine(pH-controlling agent) 1.0 part Xanthan gum (thickener) 0.3 partsDiethylene Glycol 15.0 parts Water 77.3 parts

The colorant and various additives were added to a part of the solventmentioned above. Apart from this, the thickener was added to the otherpart of the solvent. These were mixed and stirred for 1 hour to preparea shear-thinning aqueous ink C.

The viscosity of the ink, measured with an EMD-type rotary viscometer(Toki Sangyo's RE-80R with a standard rotor) at 20° C., was 41.0 mPa·sat 100 rpm, and the shear-thinning index thereof was 0.25.

Preparation of Ink Follower:

15 parts of a thickener, fatty acid amide was added to 85 parts of abase oil, polybutene, and kneaded in a three-roll mill to prepare an inkfollower 1.

Measured with a rheometer [Paar Physica's DSR4000 with a 2-degree coneplate (diameter, 25 mm)] at 20° C., tan δ of the ink follower exceeded 1at 100 rad/s.

Preparation of Ink Follower:

5 parts of a thickener, hydrophobic silica was added to 95 parts of abase oil, dimethylsilicone oil, and kneaded in a three-roll mill toprepare an ink follower 2.

Measured with a rheometer [Paar Physica's DSR4000 with a 2-degree coneplate (diameter, 25 mm)] at 20° C., tan δ of the ink follower exceeded 1at 200 rad/s.

Preparation of Ink Follower:

5 parts of a thickener, fatty acid amide was added to 95 parts of a baseoil, polybutene, and kneaded in a three-roll mill to prepare an inkfollower 3.

Measured with a rheometer [Paar Physica's DSR4000 with a 2-degree coneplate (diameter, 25 mm)] at 20° C., tan δ of the ink follower exceeded 1at 10 rad/s.

Preparation of Ink Follower:

5 parts of fatty acid amide and 5 parts of hydrophobic silica bothserving as a thickener were added to 90 parts of a base oil, polybutene,and kneaded in a three-roll mill to prepare an ink follower 4.

Measured with a rheometer [Paar Physica's DSR4000 with a 2-degree coneplate (diameter, 25 mm)] at 20° C., tan δ of the ink follower exceeded 1at 500 rad/s.

Construction of Water-Based Ballpoint Pen:

The ink and the ink follower mentioned above were combined as in Table 1given below, and filled into a ballpoint pen refill that had beenconstructed by fitting a stainless steel tip having a 0.5-mm ball at itstop end, into one end of a polypropylene pipe (inner diameter, 3.8 mm).With that, the refill was inserted into a pen tubular member toconstruct a water-based ballpoint pen.

Thus constructed, all the water-based ballpoint pens were testedaccording to the following test methods.

Writing Test:

Every water-based ballpoint pen was tested for its touch in handwritingwith it on writing paper A (JIS P3201).

Rubbing Test:

The letters or images that had been written on writing paper

A (JIS P3201) with each water-based ballpoint pen were left as such for5 minutes, then rubbed with fingers and checked as to whether or not thepaper face around them became stained.

Ink Follow Test:

Using each water-based ball point pen, 10 circles each having a diameterof 2 cm were continuously written in one line, and this writingoperation was continued for 1 minute to complete 17 lines each with 10circles therein. All the thus-written circles were checked visually fortheir condition.

Impact Test:

With the side of the ink follower thereof facing upward, eachwater-based ballpoint pen was dropped onto a plate of Japanese cedarhaving a thickness of 30 mm from a height of 120 cm. The dropping testwas repeated three times, and every pen was checked as to whether or notthe ink flowed back in the refill thereof.

The combination of the ink and the ink follower, and the test resultsare shown in the following Table 1.

TABLE 1 Ink Writing Rubbing Ink Follow Impact No. Ink Follower Test TestTest Test 1 A 1 ∘ ∘ ∘ ∘ 2 B 1 ∘ ∘ ∘ ∘ 3 A 2 ∘ ∘ ∘ ∘ 4 B 2 ∘ ∘ ∘ ∘ 5 C 1Δ x ∘ ∘ 6 A 3 ∘ ∘ ∘ x 7 B 3 ∘ ∘ ∘ x 8 C 3 Δ x ∘ ∘ 9 A 4 ∘ ∘ x ∘ 10 B 4 ∘∘ x ∘ 11 C 4 x x Δ ∘

The meanings of the test results in Table are mentioned below.

Writing Test:

-   ◯: Ink flowed out well, and smooth writing was possible under light    writing pressure.-   Δ: Ink flowed out well, and smooth writing was possible under    relatively light writing pressure.-   X: Ink flowed out poorly in some degree, and smooth writing was not    so easy.    Rubbing Test:-   ◯: After rubbed, the paper face was not stained.-   X: After rubbed, the paper face was stained.    Ink Follow Test:-   ◯: Ink flowed out well at the start of writing, and good letters and    images were written to the last.-   Δ: Ink flowed out relatively poorly at the start of writing, and the    letters and images were partly faint.-   X: Ink flowed out poorly at the start of writing, and the letters    and images were partly cut.    Impact Test:-   ◯: No change.-   X: The interface between the ink and the ink follower became greatly    disordered, and the ink flowed back.    Preparation of Water-Based Ballpoint Pen Refill (See FIG. 1)

Water-based ballpoint pen refill 1 as shown in FIG. 1 comprisesballpoint pen tip 2 in which ball 3 is held rotatable at the top endthereof, connecting member 5 to which the ballpoint pen tip is fixed atthe front thereof, ink tube 6 to which the connecting member is fixed inthe opening of the top end and in which ink 61 and ink follower 62 arecontained, tail stopper 7 which is fixed to the opening of the back endof the ink tube, and elastic member 4 that is contained in the inside ofthe above-described ballpoint pen tip and connecting member and urgesthe ball forward.

The above-described ink and the ink follower used herein are thosedescribed in the examples of the present invention.

The above-described elastic member comprises rod 41 and coil 42 at therear and tube swelling 43 having an outside diameter larger than theoutside diameter of the coil is formed at the back end of the coil 42.

The above-described tube swelling 43 is hooked at projection 51 in theinside of the above-described connecting member.

Vent hole 71 is provided through the tail stopper.

Preparation of Water-Based Ballpoint Pen of Haunting Type (See FIG. 2)

In water-based ballpoint pen of haunting type 8 as shown in FIG. 2, clip83 that can hook the pen on a pocket of clothes is prepared on the backoutside of tubular member 81, water-based ballpoint pen refill 1 asshown in FIG. 1 is contained in the interior of the tubular member in acondition to energize the refill 1 backward with the aid of spring 82(coil spring), and ballpoint pen tip 2 is extruded outside from the holeof the top end of the tubular member by knocking the back end (knockingpart) of the tubular member forward.

In the above-described water-based ballpoint pen of haunting type, astrong shock is applied to the ballpoint pen refill when the ballpointpen tip enters the tubular member by energizing the tip backward withthe aid of the spring. However, the shock is absorbed by ink follower 62of the present invention which has viscoelasticity and the backflow ofthe ink 61 is completely prevented.

Preparation of Water-Based Ballpoint Pen of Haunt Type (See FIG. 3)

In water-based ballpoint pen of haunt type 8 as shown in FIG. 3, clip 83that can hook the pen on a pocket of clothes is formed on the forwardoutside of tubular member 81 (outside of grip of the tubular member),water-based ballpoint pen refill 1 as shown in FIG. 1 is contained inthe inside of the tubular member 81 in a condition to energize therefill 1 backward with the aid of spring 82 (coil spring), and ballpointpen tip 2 is extruded outside from the top open end of the tubularmember 81 by knocking the back end (knocking part) of the tubular member81 forward.

Particularly, the water-based ballpoint pen of haunt type 8 of thisexample can be hooked on the pocket of clothes in a condition to pointthe pen point upward since the tubular member 81 has clip 83 on theforward outside thereof. This prevents ink from oozing out of the topend in a condition to be hooked on the pocket, resulting in evading soilof the clothes.

In the above-described water-based ballpoint pen of haunt type 8, agreat shock is applied to ballpoint pen refill 1 when the ballpoint pentip 2 enters the tubular member by urging the tip backward with the aidof the spring. However, the shock is absorbed by the ink follower ofthis invention which has viscoelasticity to prevent completely thebackflow of the ink.

The invention provides a water-based ballpoint pen which has goodwriting properties in that it ensures good start in writing and givesthick letters and images under light writing pressure, and the lettersand images written with it may dry rapidly.

What is claimed is:
 1. A water-based ballpoint pen comprising: anaqueous ink; a ball; a ballpoint pen tip for holding said ball at afront end thereof and for discharging said ink from said top endportion; an ink follower following said ink with consumption of saidink; and an ink container directly containing said ink and said inkfollower and for supplying said ink to said tip, said ink containercommunicating with a rear portion of said tip, wherein the ink isselected from (i) a shear-thinning aqueous ink that has a viscosity offrom 3 to 160 mPa·s, measured with an E-type rotary viscometer at 20° C.and at 100 rpm, and has a shear-thinning index of from 0.9 to 0.99, and(ii) a non-shear-thinning aqueous ink having a viscosity of from 1 to 50mPa·s, measured with an B-type rotary viscometer at 20° C., and whereinthe ink follower comprises at least a base oil and a thickener andsatisfies that the point (ω) at which its tan δ in viscoelasticitydetermination exceeds 1 falls within a range of 20 rad/s≦ω≦450 rad/s. 2.The water-based ballpoint pen according to claim 1, wherein the base oilof the ink follower is at least one selected from polybutene andsilicone oil and the thickener thereof is at least one selected fromfatty acid amide or silica.
 3. The water-based ballpoint pen accordingto claim 1 or 2, further comprising an elastic member that urges theball toward the front end of the tip when no stress is applied to theball, and wherein the ball is retractable from the front end of the tipwhen stress is applied to the ball.
 4. The water-based ballpoint penaccording to any one of claims 1 to 3, which further comprises a solidink follower combined with the ink follower.
 5. The water-basedballpoint pen according to any one of claims 1 to 4, which furthercomprises: a ball point pen refill containing the ink container, the inkcontainer communicating with a rear portion of said tip; a tubularmember containing said ball point pen refill, wherein the tip isretractably projected from a front end of the tubular member.
 6. Thewater-based ballpoint pen according to claim 5, further comprising aspring disposed in the tubular member to urge the ball point pen refilltoward a rear portion of the tubular member, wherein the tip isprojected from the front end of the tubular member when the ball pointrefill is pressed toward the front end of the tubular member against anurging force of the spring.
 7. The water-based ballpoint pen accordingto claim 5 or 6, further comprising a clip formed on the front outsideof the tubular member.